Cubic boron nitride (cBN) is characterized by a high hardness next only to diamond, and yet not having reactivity with ferrous metals unlike diamond. Accordingly, cubic boron nitride sintered material (cBN sintered material) is used in tools for cutting ferrous materials, especially hardened steel and cast iron.
When a cutting tool is made of cBN sintered material, for example, cBN sintered material made by sintering cBN under an ultra-high pressure has been used with a metal such as cobalt (Co) and ceramics such as titanium carbide (TiC) contained as binder in a concentration from 10 to 60% by volume, according to Patent Document 1. It is also proposed in Patent Document 1 to keep the binder phase to a minimum amount and form such a structure that cBN of the rest is directly bonded with each other, in order to avoid compromising wear resistance and heat resistance of the cBN sintered material.
Recently, in the field of metal cutting, there are demands to increase the efficiency of cutting operation and provide the capability to machine hard-to-cut materials. And cBN sintered material is also required to improve wear resistance and chipping resistance, as the basic requirements. Patent Document 2 proposes a cBN sintered material wherein cBN particles are bound by a large amount of binder constituted from ceramics such as titanium carbonitride (TiCN), an intermetallic compound of Ti and Al and tungsten carbide (WC) for the purpose of improving the properties described above.
[Patent Document 1] Japanese Examined Patent Publication (Kokoku) No. 52-43846
[Patent Document 2] Japanese Unexamined Patent Publication (Kokai) No. 2003-175407